Influence of ion energies on the structure,composition, and properties of multilayer Ti–Al–Si–N ion-plasma-deposited coatings

It is established that the energy of deposited particles influences the structure, composition, and properties of multilayer nitride coatings consisting of alternating layers of nanocrystalline TiN and amorphous Si₃N₄ phases with inclusions of nanocrystalline hexagonal AlN formed at energies of titanium, aluminum, and silicon ions exceeding ~317 × 10^–19, 267 × 10^–19, and 230 × 10^–19 J, respectively. As the energy of titanium ions bombarding the substrate increases above ~512 × 10^–19 J, the phase transition from disordered TiN _x to Ti₃N₂ and the appearance of 2- to 3-nm-thick sublayers in 15-nm-thick nanocrystalline TiN _x layers take place in the coating. The maximum hardness of such coatings reaches a level of ~54 GPa.

     

Phase composition,structure, and mechanical properties of arc PVD Mo–Si–Al and Mo–Si–Al–N coatings

Using an arc physical vapor deposition process, we have produced nanostructured Mo–Si–Al coatings with a uniform distribution of equiaxed grains 8–12 nm in size and Mo–Si–Al–N coatings with a multilayer structure and a modulation period from 22 to 25 nm. The former coatings consist of MoSi₂ and Mo and the latter consist of Mo2N and amorphous Si₃N₄ and AlN. The hardness of the Mo–Si–Al–N and Mo–Si–Al coatings is 41 and 18 GPa, respectively; they are similar in resistance to elastic deformation; and the Mo–Si–Al–N coating has a considerably higher resistance to plastic deformation. The coatings have roughly identical coefficients of friction (~0.67–0.69 at 20°C and ~0.52–0.56 at 550°C), but the wear resistance of the Mo–Si–Al–N coating is higher by three and two orders of magnitude at 20 and 550°C, respectively. The coatings of the two systems exhibit good adhesion to the substrate and cohesive fracture. Partial wear of the Mo–Si–Al and Mo–Si–Al–N coatings in the course of scratch testing occurs at indentation loads of 80 and 63 N, respectively.     

Pulse electrodeposition and corrosion properties of Ni–Si3N4 nanocomposite coatings

The development of modern technology requires metallic materials with better surface properties. In the present investigation; Si₃N₄-reinforced nickel nanocomposite coatings were deposited on a mild steel substrate using pulse current electrodeposition process employing a nickel acetate bath. Surface morphology, composition, microstructure and crystal orientation of Ni and Ni–Si₃N₄ nanocomposite coatings were investigated by scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction analysis, respectively. The effect of incorporation of Si₃N₄ particles in the Ni nanocomposite coating on the micro hardness, corrosion behaviour has been evaluated. Smooth composite deposits containing well-distributed silicon nitride particles were obtained and the crystal grains on the surface of Ni–Si₃N₄ composite coating are compact. The crystallite structure was face centred cubic (fcc) for electrodeposited nickel and Ni–Si₃N₄ nanocomposite coatings. The micro hardness of the composite coatings (720 HV) was higher than that of pure nickel (310 HV) due to dispersion-strengthening and matrix grain refining and increased with the increase of incorporated Si₃N₄ particle content. The corrosion potential (E _corr) in the case of Ni–Si₃N₄ nanocomposite had shown a negative shift, confirming the cathodic protective nature of the coating.     

Laser and GTAW torch processing of Fe–Cr–B coatings on steel

A comparison has been made of the relationship between microstructure and microhardness developed by surface melting Nanosteel SHS 7170 Fe–Cr–B alloy powder onto a plain carbon steel surface. This powder was initially developed as a high velocity oxyfuel sprayed coating, giving a strength 10 times that of mild steel, and is particularly suitable for surface protection against wear and corrosion. In the present study, the alloy powder was injected into the laser melted surface, while a preplaced powder was melted using the gas tungsten arc welding (GTAW) technique. The laser track consisted of fine dendrites and needle-like microstructures, which produced a maximum hardness value of over 800 HV, while the GTAW track produced a mixture of equiaxed and columnar grain microstructures with a maximum hardness value of 670 HV. The lower hardness values are considered to be associated with dilution and grain size.     

Surface tension and density data for Fe–Cr–Mo,Fe–Cr–Ni,and Fe–Cr–Mn–Ni steels

The temperature dependence of surface tension and density for Fe–Cr–Mo (AISI 4142), Fe–Cr–Ni (AISI 304), and Fe–Cr–Mn–Ni TRIP/TWIP high-manganese (16 wt% Cr, 7 wt% Mn, and 3–9 wt% Ni) liquid alloys are investigated using the conventional maximum bubble pressure (MBP) and sessile drop (SD) methods. In addition, the surface tension of liquid steel is measured using the oscillating droplet method on electromagnetically levitated (EML) liquid droplets at the German Aerospace Centre (DLR, Cologne). The data of thermophysical properties for Fe–Cr–Mn–Ni is of major importance for modeling of infiltration and gas atomization processes in the prototyping of a “TRIP-Matrix-Composite.” The surface tension of TRIP/TWIP steel increased with an increase in temperature in MBP as well as in SD measurement. The manganese evaporation with the conventional measurement methods is not significantly high within the experiments (?_Mn < 0.5 %). The temperature coefficient of surface tension (dσ/dT) is positive for liquid steel samples, which can be explained by the concentration of surface active elements. A slight influence of nickel on the surface tension of Fe–Cr–Mn–Ni steel was experimentally observed where σ is decreased with increasing nickel content. EML measurement of high-manganese steel, however, is limited to the undercooling state of the liquid steel. The manganese evaporation strongly increased in excess of the liquidus temperature in levitation measurements and a mass loss of droplet of 5 % was observed.     

Density and thermal expansion of Cr–Fe, Fe–Ni, and Cr–Ni binary liquid alloys

Densities and their temperature coefficients of liquid Cr–Fe, Fe–Ni, and Cr–Ni binary alloys have been measured containerless using the technique of electromagnetic levitation. Data have been obtained in a wide temperature range including the supercooled region. The density measurements indicate that these binary systems have a small and positive excess volume, whereas the excess free energies are negative. The temperature coefficients of these alloys can be estimated from those of the pure components. Hence, possible contributions from the temperature dependence of the excess volume can be ignored to calculate the temperature coefficient of density.     

Investigation of novel polyurethane elastomeric networks based on polybutadiene-ol/polypropyleneoxide mixture and their structure–properties relationship

Polyurethane elastomer networks were designed and synthesized based on hydroxyl terminated polybutadiene/polypropyleneoxide (HTPB/PPO) mixtures, 2,4-toluene diisocyanate and 1,4-butanediol. Various networks with different molar ratio of HTPB to PPO (0/100, 25/75, 50/50, 75/25 and 100/0) had been prepared. Depending on the length of soft segment, average functionality of polyol mixtures, mechanical and thermal properties of samples were varied. Our observations confirmed that final properties of the networks can be attributed to two synergistic factors: (a) formation of chemical network (crosslinking) and (b) soft segment length. An optimum composition was found. This optimum composition shows that both physical (hard domains) and chemical network (crosslinking) have synergistic effects. Moreover, Flory–Hugins interaction parameters of soft and hard segments were calculated. Synthesized polyurethane elastomer networks have a structure similar to semi interpenetrating polymer networks, which is named pseudo-semi-IPN. These novel polyurethane elastomer networks show higher tensile strength and economic benefit than polyurethanes which are based on other non-polar polyols.     

Effect of molybdenum on microstructure and wear properties of Fe–Ti–Mo–C laser clad coatings

Abstract

The AISI?1045 steel surface was alloyed with preplaced ferrotitanium (Fe–Ti), ferromolybdenum (Fe–Mo) and graphite powders using a 5 kW CO₂ laser. In situ carbide reinforced Fe based surface composite coating was fabricated. The results showed that (Ti,Mo)C particles with flower-like and cubic shapes were formed during laser cladding process. The growth morphology of the reinforcing (Ti,Mo)C carbide has typically faceted features, indicating that the lateral growth mechanism is still the predominant growth mode under rapid solidification conditions. Increasing the amount of Fe–Mo in the reactants led to a decrease in carbide size and an increase in volume fraction of carbide but increased the crack sensitivity of the coating. The multiple carbides of (Ti,Mo)C created a higher microhardness and excellent wear resistance than TiC alone under dry sliding wear test condition.     

The effect of Ta on structure and magnetic properties in Fe–N films

Microstructure and magnetic properties of Fe–Ta–N alloy films near the eutatic composition were studied. The four systematic alloy films with different Ta content were prepared by reactive sputtering. The dependence of structures and magnetic properties on Ta and annealing were investigated by VSM and X-ray diffraction. It is found that Ta atoms replace Fe in α-Fe lattice and have strong affinity for nitrogen, which inhibits the formation of γ-Fe₄N phase in Fe–Ta–N films. The TaN phase precipitates in grain boundaries and suppresses the growth of α-Fe(N) crystalline during annealing. Coercivity varies with the change of microstructure.     

Investigation and improvement on structural stability and stress rupture properties of a Ni–Fe based alloy

The structural stability and stress rupture properties of a Ni–Fe based alloy, considered as boiler materials in 700 °C advanced ultra-supercritical (A-USC) coal-fired power plants, was studied. Investigation on the structural stability of the existing alloy GH984 shows that the most important changes in the alloys are γʹ coarsening, the γʹ to η transformation and the coarsening and agglomeration of grain boundary M₂₃C₆ during thermal exposure. The stress rupture strength was found to be slightly lower than the requirement of 700 °C A-USC. The fracture mode of creep tested specimens was intergranular fracture. Detailed analysis revealed that η phase precipitation is sensitive to Ti/Al ratio and can be suppressed by decreasing Ti/Al ratio. The coarsening behavior of γʹ phase is related to Fe content. Adding B and P was suggested to stabilize M₂₃C₆ and increase grain boundary strength. Based on the research presented and analysis of the data, a modified alloy was developed through changes in composition. For the modified alloy, η phase is not observed and M₂₃C₆ is still blocky and discretely distributes along grain boundary after thermal exposure at 700 °C for 20,000 h. Moreover, the creep strength is comparable to the levels of Ni-based candidate alloys for 700 °C A-USC.     

Preparation of MgH2–Ni, MgH2–Ni–Si and MgH2–Ni–Ni2Si composites by mechanochemical method and their hydrogen absorption and desorption properties

To improve kinetics for hydrogen absorption of Mg and hydrogen desorption of MgH₂, ternary composites were prepared from MgH₂, Ni and Si or Ni₂Si by a mechanochemical technique. The X-ray diffraction spectra of the resultant ternary composites after the initial hydrogen desorption treatment at 400 °C in vacuum suggested that in all composites the nanocrystalline Mg₂Ni would be formed in the intergrain region between Mg and Ni components, while in the MgH₂–Ni–Si composite the nanocrystalline Mg₂Si would also be formed in the intergrain region between Mg and Si components. However, Ni₂Si did not form any alloys with Mg. The hydrogen absorption rate at 250 °C for the MgH₂–Ni–Ni₂Si composite was comparable to that for the MgH₂–Ni and MgH₂–Ni–Si composites, while the hydrogen desorption rate at 250 °C decreased in the order of MgH₂–Ni > MgH₂–Ni–Ni₂Si > MgH₂–Ni–Si. In contrast, the hydrogen desorption rate at 220 °C for the MgH₂–Ni–Ni₂Si composite was faster than that for the MgH₂–Ni composite, suggesting that Ni₂Si was a key material in the improvement of hydrogen desorbability at lower temperatures. Moreover, the most plausible reaction model and the rate-determining process for hydrogen absorption and desorption at 250 °C were determined.     

High-temperature corrosion of electric-arc coatings sprayed from powder core wires based on the Fe–Cr–B–Al system

We study the kinetics of oxidation of electric-arc dispersion-hardened coatings of the Fe–Cr–B–Al system alloyed with 6% Ni, 3% W, 1% Mo, and 1% V by spraying from powder-core wires at 700 °C. The coatings 0.5 mm in thickness were applied to plates of low-carbon steel by using powder-core wires with a diameter of 1.8 mm developed at the Karpenko Physicomechanical Institute for the coefficient of filling of the charge equal to 20–27%. The specimens were tested for heat resistance at 700°C for 100 h. The variations of the structure of the coating in the course of its long-term high-temperature oxidation were studied in an EDX metallographic microscope with EVO-4XVP microanalytic system and by using the X-ray diffraction analysis. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 5, pp. 93–97, September–October, 2008.     

Oxidation behaviour of nanocrystalline Fe–Ni–Cr–Al alloy coatings

Abstract

Nanocrystalline Fe–Ni–Cr–Al alloy coatings with ～4 wt-%Al were produced using the unbalanced magnetron sputter deposition technique with a composite 310S stainless steel target embedded with aluminium plugs. The oxidation behaviour of the coatings was studied, during which complete external α-Al₂O₃ scales were formed. During isothermal oxidation tests at 950, 1000, and 1050°C, the oxidation kinetics followed an essentially parabolic rate law, and the oxidation constants were measured to be 2·06 × 10^-3, 4·23 × 10^-3, and 1·14 × 10^-2 mg² cm^-4 h^-1 respectively. During a cyclic oxidation test at 1000°C the α-Al₂O₃ scale showed good scale spallation resistance. The surface hardness of the coatings was measured with a Knoop indentor before and after oxidation. After oxidation, the coating surface hardness was still significantly higher than that of the uncoated specimen, demonstrating the potential this coating has in the improvement of high temperature erosion resistance.     

Effect of rolling conditions on the structure and shape memory properties of Fe–Mn–Si alloys

Lattice defects play an important role in controlling the γ → ε martensitic transformation in shape memory ferrous alloys. This work focuses on the relation between various rolling and annealing processes, the microstructure resulting from the processes, and strain recovery of two Fe–Mn–Si alloys with different stacking fault energies (SFEs). Rolling experiments, conducted over a temperature range from 20 °C to 1000 °C, produce quite different microstructures, which vary from a high dislocation density to a structure containing only few isolated dislocations. In addition, annealing temperature has a very important influence not only on the dislocation arrays but also on the stacking faults remaining in the austenite, whose density depends on the SFE value for the alloy. Within the framework of the processing parameters selected for this work, i.e. roll speed, rolling reductions, processing temperatures and schedules, rolling at intermediate temperatures and annealing at a temperature of 650 °C seem to be the most appropriate methods to obtain a microstructure favorable for a nearly full degree of shape recovery.     

Solidification microstructures selection of Fe–Cr–Ni and Fe–Ni alloys

The transition of solidified phases in Fe–Cr–Ni and Fe–Ni alloys was investigated from low to high growth rate ranges using a Bridgman type furnace, laser resolidification and casting into a substrate from superheated or undercooled melt. The ferrite–austenite regular eutectic growth, which is difficult to find in typical production conditions of stainless steels, was confirmed under low growth rate conditions. The transition velocity between eutectic and ferrite cell growth had a good agreement predicted by the phase selection criterion. Which of either ferrite or austenite is easier to form in the high growth range was discussed from the point of nucleation and growth. Metastable austenite formation in stable primary ferrite composition was mainly a result of growth competition between ferrite and austenite. For a binary Fe–Ni system, a planar metastable austenite in the steady state, simultaneous growth such as eutectic and banded growth between ferrite and austenite in an initial transient region are confirmed.     

The effect of Si and microstructure evolution on the thermal expansion properties of Fe–42Ni–Si alloy strips

An alloying element of 0–1.5 wt.% Si was added to an Fe–42%Ni system, and alloy strips were fabricated using a melt drag casting process. The effects of the Si and annealing treatments on the thermal expansion properties of Fe–42Ni alloy were investigated. The addition of Si enlarged the coexisting temperature region of the solid–liquid phase and reduced the melting point, which improved the formability of the alloy strip. An alloy containing 0.6 wt.% Si had a lower thermal expansion coefficient than any other alloy in the temperature range from 20 to 350 °C. The grain size increased with the rolling reduction ratio and annealing temperature, which caused an increase in magnetostriction and consequently a decrease in the thermal expansion coefficient of the strip. The alloy strip containing 1.5 wt.% Si had a higher thermal expansion coefficient than the alloy containing 0.6 wt.% Si because of grain refining caused by the precipitation of Ni₃Fe.     

Cryorolling effect on microstructure and mechanical properties of Fe–25Cr–20Ni austenitic stainless steel

Microstructure and mechanical properties of the Fe–25Cr–20Ni austenitic stainless steel after cryorolling with different reductions were investigated by means of optical, scanning and transmission electron microscopy, X-ray diffraction and mini-tensile testing. High density tangled dislocations and a small amount of deformation twins formed after 30% deformation. After 50% strain, a large amount of deformation twins was generated. Meanwhile, interactions between the twins and dislocations started to happen. As the strain increased to 70%, many deformation twins were produced and the interactions between the twins and dislocations were significantly enhanced. When the cryorolling was 90%, the grain size was refined to the nanometer scale. XRD analysis indicated that the diffraction peaks of the samples became broader with the strain increase. The yield strength and the ultimate strength increased from 305 MPa and 645 MPa (before deformation) to 1502 MPa and 1560 MPa (after 90% deformation), respectively. However, the corresponding elongation decreased from 40.8% to 6.4%. The tensile fracture morphology changed from typical dimple rupture to a mixture of quasi-cleavage and ductile fracture. After 90% deformation, the microhardness was 520 HV, which increased by 100% compared with the original un-deformed sample.     

Laser cladding composite coatings by Ni–Cr–Ti–B4C with different process parameters

To investigate the effect of laser process parameters on microstructure and properties of composite coating, the composite coatings were manufactured by laser cladding Ni–Cr–Ti–B₄C mixed powder on Q235 mild steel with different process parameters. The coatings are bonded with the substrate by remarkable metallurgical binding without cracks and pores. The composite coatings are consisted of in situ synthesized solid solution Ni–Cr–Fe, intermetallic compound (IMC) Ni₃Ti, Cr₂Ti, and ceramic reinforcements TiB₂, TiC. Results of scanning electron microscopy (SEM) revealed that the ceramic reinforcements became coarser with higher specific energy (E_s). There were independent ceramics TiB₂, TiC, eutectic ceramic TiB₂–TiC in coatings, and eutectic alloy–ceramic was detected. Compared with the substrate, the microhardness of coatings was increased significantly, and the maximum microhardness of coatings was approximately five times as high as the substrate. The wear resistance of coatings was improved dramatically than the substrate. Compared to the coatings with lower E_s, higher E_s led to lower microhardness and worse wear resistance ascribing to more Fe diffused into the coating from the substrate.     

Influence of ageing on wear resistance of an Fe–Mn–Si–Cr–Ni–Ti–C shape memory alloy

To further improve the wear resistance of Fe–Mn–Si–Cr–Ni based shape memory alloys, the effects of ageing at 1123 K with and without pre-deformation at room temperature on the precipitation of second-phase particles and their effects on wear resistance were investigated in an Fe–Mn–Si–Cr–Ni–Ti–C alloy. Results showed that the solution treated Fe–Mn–Si–Cr–Ni–Ti–C alloy exhibited much better wear resistance than the solution treated AISI 321 stainless steel; ageing with pre-deformation improved the wear resistance of Fe–Mn–Si–Cr–Ni–Ti–C alloy more effectively than ageing without pre-deformation, especially under the heavy load condition.     

Structure,Composition, and Properties of Arc PVD Mo–Si–Al–Ti–Ni–N Coatings

Using an arc physical vapor deposition process, we have produced nanostructured Mo–Si–Al–Ti–Ni–N coatings with a multilayer architecture formed by Mo₂N, AlN–Si₃N₄, and TiN–Ni and a crystallite size on the order of 6–10 nm. We have studied the physicomechanical properties of the coatings and their functional characteristics: wear resistance, adhesion to their substrates, and heat resistance. According to high-temperature (550°C) wear testing and air oxidation (600°C) results, the coatings studied here are wearand heat-resistant under appropriate temperature conditions. Their properties are compared to those of Mo–Si–Al–N coatings.